In known devices of this sort, the various alpha-numeric and other symbols to be used are visibly displayed on the tops of keys which are arranged in prescribed order in a matrix of rows of ten or more keys each. The key tops are kept horizontal, and the rows further from the operator are at successively higher levels. The operator's hands are suspended over the matrix or keyboard so that the fingertips rest lightly on a set of "home" keys which are aligned in a central row or tier in the matrix. Keys are operated by downward movement of particular fingers individually in a learned procedure. To operate keys on other rows, the entire hand is moved to learned alternate positions, so that the specified fingers are over intended alternate keys. If the hand is not moved correctly, however, the fingers may not in fact be positioned over the desired alternate keys, so that when a finger is moved, an entry error is caused. Similarly, upon return to the home keys, if the hand motion is slightly in error, the fingers may not be positioned over the home keys in the proper fashion, so that successive entries may also be in error. To verify finger and key relationships, many operators resort to watching their fingers over the keys, so as to assure correct entry. This hand movement to operate other keys and return to the home key position, and this tendency to observe the keys as well as the material to be entered, slow the entry of data or signals into the device.
A similar problem exists with numerical keyboards which consist of ten digital entry keys and function control keys. With these devices, home keys are not used and different keys are frequently operated by the same finger, which is guided visually. The operator must constantly observe the keyboard to assure correct entry. Eye movement between the data to be entered and the digital keyboard, and use of only a few fingers, slow the entry process, and inattention to finger placement causes entry errors.